Currently the tetmesh tally option is only available in DAG-MCNP5/6, but there
are plans to expand this to all the codes that DAGMC currently supports.

Once you have used the above instructions to produce one or more meshes in .h5m
format, you must specify to MCNP that your tally is a tetmesh tally. This is
done by putting special keywords on the tally comment (FC) line. For example,
adding the following lines to an MCNP input file would tell MCNP that tally 4 is
a tetmesh tally, that the input mesh file is mesh.h5m, and the results
should be stored in mesh_out.h5m.

The kernel density estimator tallies are a suite of tallies that allow scoring
to be done using the vertices of a tetmesh or add additional mesh-based scoring
such as collision estimator tallies. The theoretical details behind KDE tallies
can be found in Kerry Dunn’s Ph.D. thesis.